The Jahn–Teller and related effects in the cyclopentadienyl radical. I. The ab initio calculation of spectroscopically observable parameters

Abstract

Ab initio calculations are performed for the X 2 E 1 and A 2 A 2 states of the cyclopentadienyl radical. An important goal of these calculations is to guide the analysis of the experimentally observed A 2 A 2-X 2 E 1 electronic spectrum. Vibrational frequencies for both theX andà state are reported. Large changes in frequency between the states for out-of-plane vibrations are found, leading to the expectation that overtones of these modes will appear strongly in the spectrum. Additionally, spectroscopically obtainable parameters describing the Jahn-Teller effect are calculated for theX state. Using all this information theX −à electronic spectrum is predicted for both C5H5 and C5D5.

A Joint Experimental and Computational Study of the Negative Ion Photoelectron Spectroscopy of the 1-Phospha-2,3,4-triazolate Anion, HCPN3–

“…The best fit of the simulated NIPE spectrum to the experimental spectrum indicates that the ground state of HCPN 3 • is a 5π-electron 2 A″ π radical state, with a 6π-electron, 2 A′, σ radical state being at most 1.0 kcal/mol higher in energy.…”

“…19 The IE of (CH) 2 20 Comparisons of the (CH) 2 N 3 anion and radical with the previously studied (CH) 4 N 21 and (CH) 3 N 2 22,23 species found that substitution of each CH group in C 5 H 5 −/• by an isoelectronic N atom has a significant effect on the chemistry and thermodynamic properties, such as the C−H bond dissociation energies and gas-phase acidities, of these three nitrogen-containing analogues of C 5 24 This anion can be viewed as the n = 1 member of the series, (CH) 2-n P n N 3 − (n = 0−2). Nucleus-independent chemical shift (NICS) and quantum theory of atoms in molecules (QTAIM) calculations showed that HCPN 3 − is aromatic, with its aromaticity being intermediate between that of the n = 0 [(CH) 2 N 3 − ] and the n = 2 (P 2 N 3 − ) members of this series. In this paper we report the detailed results of NIPE spectroscopy and electronic structure calculations on HCPN 3 − and the neutral radical formed from it.…”

On the construction of quasidiabatic state representations of bound adiabatic state potential energy surfaces coupled by accidental conical intersections: Incorporation of higher order terms

“…This molecule falls in the class of nitrogen containing five member ring compounds known as azolyls and can be viewed as a derivative of the well studied Jahn-Teller radical (CH) 5 , cyclopentadienyl, [16][17][18] which has a degenerate 2 E ′′ 1 ground electronic state derived from π orbitals. In triazolyl the minimum energy conical intersection (MEX) and minimum on the ground state potential energy surface, both of which have C 2v symmetry, are relatively well separated.…”

Explorations of conical intersections and their ramifications for chemistry through the Jahn–Teller effect

“…The key to understanding the spectra is a good estimate of the D's and ω's obtained using high level ab initio calculations. 18 Indeed, prior to these calculations the parameter space had proven far too great for a successful analysis of the spectra. …”